There are two kinds of charcoal: black charcoal and white charcoal. The black charcoal is produced by carbonizing Japanese oaks such as nara and kunugi in a charcoal kiln at 400-700° C. before being cooled in the kiln, whereas the white charcoal, especially Kinokuni bichoutan (charcoal), is produced by carbonizing Quercus Phillyraeoides (a kind of beech) in a charcoal kiln at 800-1000° C. before being rapidly cooling outside the kiln. The charcoal kiln above is a kind of kiln in which material is heated in the absence of air and the smoke produced during the combustion of wood is discharged directly outside. The smoke is a product resulting from the thermal decomposition of cellulose accounting for 75% of the ingredients of the wood and of lignin accounting for 20-25% thereof. On the other hand, though most of the wood-based waste materials such as waste building material are disposed of by incineration, dioxin is generated by directly combusting the waste wood-based material because chlorine synthetic resin may be intermingles with the waste material. Consequently. there arise a problem of atmospheric pollution when the combustible gas is discharged and another problem of disposing the ashes produced by incineration. In the conventional carbon production method above, moreover, it takes several days combusting the wood completely after the construction of the kiln is started and also takes a great deal of labor and time; the problem is that the production method is not fit for short-term mass production.
Further, a combustion furnace for directly combusting a material by a natural draft accompanied by partially gasified combustion is disclosed in JP-A-11-63445. As shown in FIG. 7, the combustion furnace described in JP-A-11-63445 mainly comprises an accumulated gas gasification chamber 51 having an upper opening, a first combustion chamber 52, a second combustion chamber 56 and an exhaust pipe 58. The combustion furnace attended with gasification combustion is provided with the accumulated gas gasification chamber 51 communicating with the first combustion chamber 52 having an ignition door 53 and a first air damper 54 in the lower portion in order to store an incineration material 59 and to convert part of the material 59 into combustible gas, and the second combustion chamber 56 communicating with the first combustion chamber 52 via a fire grate 55 and having the exhaust pipe 58 in the upper portion and a second air damper 57 in the lower portion. Although the combustion furnace above is capable of completely combusting the material so as to prevent the generation of a cloud of dust as well as an offensive smell, this system is basically different from a smokeless porous carbon production system according to the invention in that the former is characterized by completely combusting a material so as to reduce the material to ashes, whereas the latter is intended for porous carbon production. In other words, the material charging opening of the combustion furnace above is open and the material 59 is completely combusted and reduced to ashes because a large amount of air is introduced into the furnace from the charging opening and the dampers for combusting purposes. Moreover, the combustion furnace has no equipment for use in cooling or radiating heat of a carbide to be taken outside when the nature of an incinerator is considered.